The invention relates to an apparatus for use in the agricultural field for spreading powdered or granular substances such as fertilizer or chemicals, onto a field. The invention also relates to an apparatus for distributing seeds onto a field.
To achieve improved productivity and yields, modern agricultural practices utilize fertilizers, pesticides and other chemicals which must be applied to the fields or the crops grown in the fields. Such substances are commonly applied utilizing a vehicle or a towed implement which has a hopper or box for carrying the material to be distributed and a distribution means. There are a variety of types of distribution means known and commercially used. For example, spinner mechanisms have been used in which a rotating spinner is positioned near a controlled discharge opening from the box containing the substance to be distributed. As the substance strikes the spinner, it is thrown outwardly. However, this type of apparatus is less than ideal for a material that varies in particle size since the larger particles will be thrown a greater distance. Commonly, blended materials must be distributed, and spinner type machines may produce patterns of distribution that are chemically unacceptable. Also, spinner type machines are susceptible to wind-produced pattern errors, as well as errors in distribution patterns produced by the rolling motions of the vehicle. Spinner-type distributing machines are also highly susceptible to errors of the vehicle operator since there is not any practical way to mark the path where the material has been distributed. This may result in excessive overlap or bands over which no material has been distributed. In addition, spinner-type machines are not well suited to grain seeding applications, particularly to low seeding rates of fine seeds.
There are also known and used boom-type spreaders in which a boom is mounted at the rear of the vehicle transversely to the direction of travel. These boom-type spreaders generally carry the material through the boom by a mechanical conveyor, such as an auger. The material is then dropped from the boom through spaced openings. Machines of this type are mechanically complex and are prone to maintenance problems. They are also susceptible to wind-produced errors since the material free-falls usually a distance of five to six feet. Also, the boom-type mechanical spreaders are totally unsatisfactory for distributing materials that are a blend of different particle sizes since the larger particles will be carried to the outer end of the boom while the fines are dropped along the inner portions of the boom. The same disadvantage occurs for non-blended products unless particle size is closely controlled. Moreover, boom-type mechanical spreaders are not suitable for seeding work, particularly the seeding of small seeds at low rates.
To overcome the difficulties of the spinner-type and boom-type mechanical spreaders, there have been developed distribution systems in which air is used as the distributing medium. There are a number of air spreaders which are known and commercially used, and their capability and effectiveness depends on the particular design. An early such design is shown in U.S. Pat. No. 3,606,097. Air spreaders generally require more power than other types of distribution systems, and especially critical is the design of the air system. Each time that the air stream makes a turn, this adds significantly to power requirements. Moreover, the path of the material being carried by the air stream should always be level or downward, since conveying material upwardly with an air stream requires a large amount of power.
There are two overall configurations of air spreaders that are known and used. One such configuration mounts the distribution boom toward the middle of the vehicle ahead of the material hopper while the other configurations mounts the boom at the rear of the vehicle. Although the configuration in which the boom is mounted forwardly of the material storage hopper provides better weight distribution and better vision by the operator, midship mounted booms require an additional rear mounted center section and also will leave a "dead spot" at the corners of the fields.
Rear mounted booms of known air spreaders generally have complex material distribution systems in an attempt to introduce the material evenly into the air stream to provide uniform distribution patterns. Air spreading machines which attempt to divide the material that is already moving in the air stream are not satisfactory and provide unsatisfactory distribution patterns. Other distribution configurations attempt to mechanically convey the material from the material hopper and mechanically divide the material before it enters the air stream. Examples of such distribution systems are shown in U.S. Pat. Nos. 4,462,550, 4,475,819 and 4,489,892.
There are other desirable features of air distribution systems which prior art systems have been unable to achieve satisfactorily. Particularly in rolling fields, it is highly desirable to have the ability to raise or lower each half of the boom independently of the other. Also, the booms must be designed so as to be positioned out of the way during over the road transportation and during storage of the vehicle without elevating the boom to an undesirable height while still maintaining the boom at an optimum spreading height. No known boom-type air spreaders have been able to achieve this without complicating the air distribution system.
There is therefore a need for an improved apparatus for spreading a variety of granular and powdered products utilizing air as the conveying medium, which improved apparatus will overcome the deficiencies of known apparatus of this type.